1. Field of the Invention
The present invention relates to an electronic control unit having a microprocessor built-in for use in, for example, a fuel supply control of an automobile engine and, more particularly, to improvement of an on-vehicle electronic control unit including a plurality of control circuit sections electrically divided so as to carry out mutual communication of serial signals.
2. Description of the Related Art
On-vehicle electronic control unit in which information exchange by a method of serial communication is carried out among a plurality of microprocessors sharing functions, and communication error is detected to carry out error processing, has been practically and widely used in various fields.
For example, according to the Japanese Patent Publication (unexamined) No. 108835/2002, the following “On-Vehicle Electronic Control Unit” is proposed. This on-vehicle electronic control unit comprises serial communication means that is constituted of a main CPU and a sub CPU, and is capable of transferring a control constant at the time of start of operation and mutually communicating a variety of data during the operation freely. Further disclosed in this on-vehicle electronic control unit are means for sum check error and retransmission processing relative to serial communication data, means for timeout check error and reset processing of microprocessor, or means for inhibition processing of control output.
According to the Japanese Patent Publication (unexamined) No. 333901/2002, another “On-Vehicle Electronic Control Unit” is proposed. This on-vehicle electronic control unit comprises serial communication means that is constituted of an integrated circuit section having a microprocessor and a communication control circuit, and is capable of transferring a control constant at the time of start of operation and mutually communicating a variety of data during the operation. In this on-vehicle electronic control unit, an example of a communication packet arrangement is described in detail.
On the other hand, according to the Japanese Patent Publication (unexamined) No. 162814/No. 9, the following “Communication Monitoring Unit” has been proposed. This communication monitoring unit comprises a communication control section that controls data communication and outputs an error notification signal upon detecting any communication error, an error counter that counts up in response to the input of the mentioned error notification signal, and an annunciation section that announces a communication error in response to the fact that a count value of this error counter has reached a plus predetermined value (threshold). In this communication-monitoring unit, there is provided counter subtraction means that counts down a count value of the mentioned error counter upon the fact that the control of data communication is normally carried out in the mentioned communication control section. Further it is arranged so as to prevent an alarm generation in vain with respect to a sporadic and chronic error in which an error state automatically recovers, while immediately making an annunciation with respect to a fatal and continuous failure.
As for the rest, associated with this invention, according to the Japanese Patent Publication (unexamined) No. 235598/2002, the following “Vehicle Control Unit” is proposed. In this vehicle control unit, there are proposed error occurrence storage means and drive-stopping means of a specified electrical load that bring any microprocessor such as main CPU or sub CPU contained in an on-vehicle electronic device in a save operation state, when the microprocessor runs away, and then restarts the microprocessor.
According to “On-Vehicle Electronic Control Unit” of the Japanese Patent Publication (unexamined) No. 108835/2002, five types of packets of A•control constant transmission, B•transmission of regular data, C•transmission of irregular data, D•transmission of readout request command, E•transmission of required data are applied in the communication from a main CPU to a sub CPU (hereinafter referred to as downstream communication).
Likewise, in the communication from a sub CPU to a main CPU (hereinafter referred to as upstream communication), all the communication packets of B-E, except for A•control constant transmission, are applied on an equal basis.
Furthermore, a receiving confirmation reply or a retransmission request can be made with respect to each of the upstream and downstream communications, so that an extremely high degree of freedom is achieved. A problem, however, exists in that a communication jam-up takes place at the time of occurrence of some sort of communication error making it incapable to carry out transmitting and receiving an essentially required data.
According to “On-Vehicle Electronic Control Unit” of the Japanese Patent Publication (unexamined) No. 333901/2002, types of a communication packet is enormously reduced. In this control unit, 5 types of communication packets of A•control constant transmission, B•whole input readout request, C•whole output transmission, D•specific input readout request specifying an address, E•specific output transmission specifying an address as a downstream communication are applied from a master station to a sub station; while no spontaneous upstream communication packet from the sub station to the master station is prepared.
Accordingly, reporting from the sub station cannot be carried out without request from the master station, and therefore a regular request comes to be necessary in the case of presence of any regular report data, eventually resulting in a problem that unnecessary downstream communication takes place.
According to “Communication Monitoring Unit” of the Japanese Patent Publication (unexamined) No. 162814/1997, there remain the following problems. That is, a problem exists in that in case of setting a threshold for determining an error to a large value, any response delay is generated in detection of error occurrence subsequent to a normal communication. On the other hand, in case of setting a threshold for determining an error to a small value, too-sensitive error detection is carried out even when any slight and sporadic error occurs.
Moreover, response to a variety of numerous communication errors and processing of timeout error or retransmission are not described from a comprehensive viewpoint.
According to “Vehicle Control Unit” of the Japanese Patent Publication (unexamined) No. 235598/2002, a problem exists in that although timeout in communication can be detected by monitoring the run-away of a microprocessor, communication error in terms of lack or mix in bit such as sum check error is not monitored.